Radio-frequency-energy transmission-line system and antenna



May 30, 1961 LAN J. CHU ET AL RADIO-FREQUENCY-ENERGY TRANSMISSION-LINE SYSTEM AND ANTENNA 2 Sheets-Sheet 1 Filed June 26, 1956 FIG.4

4! I I! llllll ltnl|ulm FIGJ INVENTORS LAN JEN CHU BY IVAN M-FAIGEN FIG.2

LAN J. CHU ET AL RADIO-FREQUENCY-ENERGY TRANSMISSION-LINE May 30, 1961 SYSTEM AND ANTENNA 2 Sheets-Sheet 2 Filed June 26, 1956 FlG.7

\INVENTORS LAN JEN CHU BY IVAN M.FA|GEN ATTORNEYS United States Patent RADIO-FREQUENCY-ENERGY TRANSMISSION- LINE SYSTEM AND ANTENNA Lan J. Chu, Lexington, Mass., and Ivan M. Faigen, Wayland, Mass. (both of 634 Waverly St., Framingham, Mass. assignors, by mesne assignments, of one-twelfth to Robert H. Rines, Belmont, Mass.

Filed June 26, 1956, Ser. No. 594,065

18 Claims. (Cl. 343-859) The present invention relates to radio-frequency-energy transmission-line systems and antennas and, more particularly, to systems and antenna structures adapted for use as beacons and similar antennas.

In many radio-frequency antenna transmitting systems, an omni-directional horizontal radiation pattern and a high-gain vertical radiation pattern are required to provide uniform broadcasting in all directions of azimuth and over a desired field of coverage. Many antennas have been designed for producing such patterns. Some of these antennas are in the form of arrays of vertically stacked linear elements; others are in the form of loops; still others employ antennas of various other configurations, including antennas embodying a plurality of angularly disposed slot radiators, wave guides or horns. Antennas of this character, however, are quite costly to manufacture and usually require large numbers of cumbersome and expensive insulators which are subject to periodic deterioration under the influence of atmospheric conditions. Such antennas generally also require phaseand impedance-correcting networks and other devices associated with the feed transmission lines that add cost and complexity to the equipment. Not only is it desirable to reduce the cost of manufacture of such antennas, therefore, but it is quite advantageous to eliminate the necessity for the use of insulators and such phaseand impedancecorrecting devices.

An object of the present invention, accordingly, is to provide a new and improved antenna that is particularly adapted for use at high power and that produces high gain consistent with broad-band performance; the antenna being free of the above-described disadvantages and eliminating the necessity for copious insulators and special phaseand impedance-correcting devices.

An additional object is to provide such an antenna that is particularly adapted for operation as a beacon antenna.

Still an additional object is to provide an antenna that is completely enclosed and thus not subject to the elements, and that is of rugged and simple construction comprising a radiating preferably cylindrical mass structure that houses a simple balanced transmission-line system adapted to produce the desired performance.

Still an additional object is to provide such an antenna that is inexpensive to manufacture and maintain.

Prior-art antennas, such as those before referred to, moreover, invariably utilize balanced-to-unbalanced transmission-line feed systems. If, for example, a coaxialline transmission-line feed is to be connected to antenna radiating elements, the problem of balancing the unbalanced coaxial line to the balanced radiating structure presents itself. Various expedients, such as quarter-wave stubs, counter-poises, bazooka devices and similar compensatory structures have been employed to attempt to effect such an unbalanced-to-balanced line connection. From a broader aspect, the present invention provides a new and improved transmission-line system that enables the transition from an unbalanced to a balanced line without the necessity for such compensatory structures.

Other and further objects will be explained hereinafter and will be more particularly pointed out in the appended claims.

The invention will now be described in connection with the accompanying drawing,

Fig. 1 of which is a side elevation, partly cut away to illustrate details of construction, showing the invention in preferred form;

Fig. 2 is a longitudinal section taken upon the line 22 of Fig. 1, looking in the direction of the arrows;

Fig. 3 is a fragmentary section taken upon the line 3-3 of Fig. 1, looking in the direction of the arrows, and drawn upon an enlarged scale;

Fig. 4is a transverse section of enlarged scale taken upon the line 4-4 of Fig. 2, looking in the direction of the arrows;

Fig. 5 is an enlarged perspective view of an antenna element;

Fig. 6 is an enlarged view of the lower portion of the system of Fig. 2; and

Fig. 7 is a perspective View of a modification.

Referring to Figs. 1 and 2, the high-power, high-gain, broad-band antenna of the present invention is enclosed within a cylindrical housing, mast or column 1 which may be a Fiberglas or other insulating cylinder. Within the Fiberglas housing or mast 1, a plurality of successive cylindrical sleeve dipole antenna elements are disposed at 3, 3', 3", 3", providing radiation in all directions of azimuth and, depending upon the number of antenna elements, providing the desired degree of vertical radiation directivity or non-directivity. The transmission-line system for propagating the radio-frequency energy that may either be fed from a transmitter to the antenna elements 3, 3', 3", 3'" to enable them to radiate into space, or may be fed from the antenna elements 3, 3', 3", 3" to a receiver, extends within and along the illustrated vertical direction of the sleeve antenna elements. That transmission-line system comprises at its lower end an unbalanced coaxial transmission line having an outer conductor 5 and a coaxially-disposed inner conductor 7, insulated therefrom at 9, as more particularly shown in Figs. 3 and 4. The insulation 9 may be a solid dielectric material or it may be air or other gas maintained at any desired pressure. The coaxial line 5, 7 is provided at its lower end, Figs. 2 and 6, with a connector 4 for connecting the same to a transmitter or receiver 2. Such an unbalanced type line, of course, if it is to be connected to a balanced transmission line that, in turn, is connected to the dipole antenna elements, would ordinarily require the before-mentioned prior-art compensating stubs and other devices which, however, the present invention renders unnecessary. The balanced transmission line is shown comprising a pair of vertically extending substantially parallel transmission lines 11 and 13 surrounded by the antenna sleeves 3, 3, etc. and supported spaced from one another by insulating spacers 15. The transmission lines 11 and 13 may be of any desired cross-section but they are illustratively shown as of hollow square cross-section.

In accordance with the present invention, the transition from the unbalanced coaxial line 5, 7 to the balanced line 11, 13 is effected by extending the line 5, 7 upward within the hollow line 11 to an aperture 17, Fig. 3, at a predetermined point along the hollow conductor 11. The inner conductor 7 is then connected by a single-conductor extension 7' through the aperture 17 in a direction preferably substantially normal to the vertical direction of extension of the balanced lines 11 and 13; i.e., horizontally. An insulating spacer sleeve 15 may, if desired, cover the extension 7'. The single-conductor extension 7 of the inner conductor 7 of the coaxial line 5, 7, terminates at 19 upon acorresponding point of the other line 13 of the. pair of balanced lines 11, 13, thereby to excite the line 13.

Such a connection by itself, however, would be subject to the disadvantages of all unbalaneed-line-to-balancedline connections and would normally require the use of the compensating devices before referred to. In accordance with the present invention, however, the extension 7' is made extremely short, namely, of length less than substantially one-eighth of the wavelength of the energy with which the line is to operate and preferably of length corresponding to about one-sixteenth of the wavelength, or less. Through this expedient, the phase of the energy fed along the extension 7 to the transmission line conductor 13 will not materially vary along the extension 7'. By then insuring that the current flowing along the outer line conductor 5 of the coaxial line 5, 7 exerts no infiuence on the field between the parallel-line conductors 11 and 13, balanced currents may be set up along the line conductors 11 and 13 to effect a satisfactory balancedto-unbalanced transmission-line transition. This end is achieved by electrically connecting the outer line conductor 5 of the coaxial line 5, 7 to the inner surface 21 of the hollow line conductor 11, preferably substantially throughout the coextensive portions of the same, as at 6, Figs. 3 and 4. If desired, of course, the inner surface 21 of the hollow line conductor 11 and the electrically contiguous outer-line conductor 5 of the coaxial line 5, 7 may constitute but a single common conducting surface. The balanced lines 11 and 13 themselves are shown connected at appropriate wavelength intervals 23 and 25 so that the energy fed from the coaxial line 5, 7 may enable the setting up of the necessary field along the balanced conductors 11 and 13 to produce balanced energy feed to or from the antenna elements 3, 3', 3", 3", etc. This feed may be effected by providing conductors extending from the lines 11 and 13 to lips 30, 30' and 30", 30" upon the adjacent edges of the respective dipole sleeve antenna elements 3, 3' and 3", 3". Conductors 24 and 26 thus extend from the respective lines 11 and 13, preferably normal to the plane of the transmission line 11, 13, to connect with the respective antenna sleeves 3, 3" and 3! 3/!!- Not only is the antenna structure of the present invention simplified through the utilization of minimal connections for effecting balanced-to-unbalar1ced-line feed, but the actual length of required over-all transmission-line is inherently kept to a minimum. This structure, moreover, so long as the extension 7 is of small dimensions, will effect the balanced-to-unbalanced transition over relatively wide frequency ranges. A further feature of this construction resides in the fact that an additional array of similar antenna elements may, if desired, be stacked directly upon the antenna of Figs. 1 and 2. Since the coaxial line 5, 7 is disposed within only the hollow conductor 11, a similar coaxial-line feed may be disposed within the other hollow conductor 13 to feed an upper antenna section substantially identical with the antenna of Figs. 1 and 2. Such a result would be desirable for purposes of duplexing, relaying or where one array is desired for reception and the other array for transmission.

If, however, more than two antennas of this type are to be stacked one on top of the other, limitations are introduced upon the band of frequencies over which the antenna may effectively operate. Where greater numbers of antenna radiators are desired, therefore, it is preferable that a structure such as that shown in Fig. 7 be employed. In Fig. 7, as before suggested, the outer conductor 5 of the coaxial line 5, 7 is shown constituted of the inner wall 21 of the parallel conductor 11. In this case, the parallel hollow conductor 11 is of greater diameter than the other parallel conductor 13 disposed to one side thereof, shown to the right. The extension 7' of the inner conductor 7 of the coaxial line 5, 7, is shown connected to an intermediate point 19 of the transmission-line conductor 13. The upper and lower ends of the vertical transmission-line conductor 13 are shown provided with preferably arcuate transverse portions or connections 33 and 35 which connect at intermediate points 37 and 39 with further vertical extensions of the transmission-line conductor 13 shown, respectively, at 13 and 13". The transmission-line extensions 13' and 13", however, are disposed on the opposite side of the larger cross-section hollow conductor 11 from the right-hand side location of the conductor 13 itself. In such a case, the transmission-line extensions 13 and 13" are shielded by the larger hollow conductor 11 from the other balanced line conductor 13. The transmission-line section formed by the lower portion of the line conductor 11 and the extension 13 is thus shielded from the transmission-line section formed by the conductor line 11 and the conductor line 13, which, in turn, is also shielded from the further transmission-line section formed by the upper line-conductor extension 13" and the upper portion of the line conductor 11. By this expedient, the wide-band characteristics of the antenna are maintained even through a large number of antenna elements 3, 3', 3", 3", 103, 103', 103", 103', etc. may be employed. The antenna elements 3', 3", 103 and 103" are excited by the connections 24 from the hollow conductor 11. The antenna elements 3 and 3", on the other hand, are respectively connected to the lower and upper ends 113 and 123 of the line extension 13. The antenna sleeves 103 and 103" are similarly energized by the respective lower and upper ends 113 and 123 of the transmission-line extension 13".

While the antennas of Figs. 1 and 7 will produce excellent horizontal omnidirectionality and the desired vertical coverage, they are incapable, of course, of radiating directly upward. This additional result may, however, easily be effected by, for example, tapping a further extension 53 onto the conductor 13 to feed, for example, an upwardly directed helical or other antenna array 55.

The Fiberglas or other housing of the antenna may be capped at the ends to provide a sealed extremely lightweight and rugged unit. The unit, exclusive of its mounting, for example, may be approximately eight inches in diameter and twelve feet in length in which event it is found to weigh less than a hundred and fifty pounds. All of the metallic parts may be maintained at directcurrent ground potential by grounding the same to afford lightning protection. The enclosed type of design, moreover, precludes much of the trouble ordinarily encountered due to rough or poor handling or adjustment in field operations, particularly where the antenna may be utilized for portable operations. The design, moreover, affords maximum weather protection, and is extremely easy for field assembly and installation by untrained crews. The power handling capacity is extremely high, being limited only by the transmission-line voltage break-down itself. If desired, upward beam tilt may be provided in the vertical pattern by appropriately phasing successive sections of the dipole elements. As an illustration, uniform phase variation of approximately 12 /2 degrees between antenna dipole elements will provide a suitable upward beam tilt. The length-to-thickness ratio of the antenna radiating sleeve elements themselves may be approximately 2.5 to 1, more or less, with the unobstructed radiating cylinders providing a pattern having excellent circularity over a broad band of frequencies. The thickness of the antenna elements of this character, moreover, provides excellent impedance-matching potentialities.

Further modifications will occur to those skilled in the art and all such are considered to fall within the spirit and scope of the invention, as defined in the appended claims.

What is claimed is:

l. A system for propagating radio-frequency energy of a predetermined wavelength having, in combination, an unbalanced two-conductor transmission line, a balanced two-conductor transmission line, means for connecting one conductor of the unbalanced line by a single-conductor path of length less than an eighth of the said wavelength to one of the conductors of the balanced line at an intermediate point therealong that, with respect to the said one conductor of the unbalanced line, is substantially electrically symmetrically disposed between the ends of the said one conductor of the balanced line, the said ends each being terminated in similar radiating elements to present substantially the same impedance at the said intermediate point, and means for providing an electrical path between the other conductors of the lines, the said path being disposed in a region electrically isolated from the radio-frequency field between the conductors of the balanced line in order to prevent current flowing along the other conductor of the unbalanced line from influencing the radio-frequency field between the conductors of the balanced line.

2. A system for propagating radio-frequency energy of a predetermined wavelength having, in combination, an unbalanced coaxial transmission line, a balanced parallel-conductor transmission line, means for connecting the inner conductor of the coaxial line by a singleconductor path of length less than an eighth of the said wavelength to one of the conductors of the parallel-conductor line at an intermediate point therealong that, with respect to the said conductor of the unbalanced line, is substantially electrically symmetrically disposed between the ends of the balanced line, the said ends each being terminated in similar radiating elements to present substantially the same impedance at the said intermediate point, and means for providing an electrical path between the other conductors of the lines, the said path being disposed in a region electrically isolated from the radiofrequency field between the conductors of the balanced line in order to prevent current flowing along the outer conductor of the coaxial line from influencing the radio frequency field between the conductors of the balanced line.

3. A system for propagating radio-frequency energy of a predetermined wavelength having, in combination, a pair of parallel conductors providing a balanced transmission line and at least one of which is hollow, an unbalanced coaxial transmission line disposed within the said one hollow conductor and extending coextensively therewith to a predetermined intermediate point thereof, an aperture in the said one hollow conductor near the said predetermined point that, with respect to the inner conductor of the said coaxial line, is substantially electrically symmetrically disposed between the ends of the other of the pair of parallel conductors of the balanced line, the said ends each being terminated in similar radiating elements to present substantially the same impedance at the said predetermined intermediate point, a singleconductor path extending from the inner conductor of the coaxial line through the aperture to a corresponding point of the other of the pair of parallel conductors, and the inner surface of the said one hollow conductor and the coextensive outer conductor of the coaxial line being electrically contiguous.

4. A system for propagating radio-frequency energy of a predetermined wavelength having, in combination, a pair of parallel conductors providing a balanced transmission line and at least one of which is hollow, an unbalanced coaxial transmission line disposed within the said one hollow conductor and extending coextensively therewith to a predetermined intermediate point thereof that, with respect to the inner conductor of the said coaxial line, is substantially electrically symmetrically disposed between the ends of the other of the pair of parallel conductors of the balanced line, the said ends each being terminated in similar radiating elements to present substantially the same impedance at the said predetermined intermediate point, an aperture in the said one hollow conductor near the said predetermined point, a singleconductor path extending from the inner conductor of the coaxial line through the aperture to a corresponding point of the other of the pair of parallel conductors and of length less than an eighth of the said wavelength, and the inner surface of the said one hollow conductor and the coextensive outer conductor of the coaxial line being electrically contiguous.

5. A system for propagating radio-frequency energy of a predetermined wavelength having, in combination, a pair of parallel conductors providing a balanced transmission line extending along a predetermined direction, and at least one of which is hollow, an unbalanced coaxial transmission line disposed within the said one hollow conductor and extending coextensively therewith to a predetermined intermediate point thereof that, with respect to the inner conductor of the said coaxial line, is substantially electrically symmetrically disposed between the ends of the other of the pair of parallel conductors of the balanced line, the said ends each being terminated in similar radiating elements to present substantially the same impedance at the said predetermined intermediate point, an aperture in the said one hollow conductor near the said predetermined point, a conductor of length less than an eighth of the said wavelength extending from the inner conductor of the coaxial line through the aperture substantially normal to the said predetermined direction and terminating upon a corresopnding point of the other of the pair of parallel conductors, and the inner surface of the said one hollow conductor and the coextensive outer conductor of the coaxial line being electrically contiguous.

6. A system for propagating radio-frequency energy of a predetermined wavelength having, in combination, an unbalanced two-conductor transmission line, a balanced two-conductor transmission line, means for connecting one conductor of the unbalanced line by a single-conductor path of length less than an eighth of the saidwavelength to one of the conductors of the balanced line at an intermediate point therealong that, with respect to the said one conductor of the unbalanced line, is substantially electrically symmetrically disposed between the ends of the balanced line, the said ends each being terminated in similar radiating elements to present substantially the same impedance at the said intermediate point, means for providing an electrical path between the other conductors of the lines, the said path being disposed in a region electrically isolated from the radio-frequency field between the conductors of the balanced line in order to prevent current flowing along the other conductor of the unbalanced line from influencing the radio-frequency field between the conductors of the balanced line, the radiating elements being external to the balanced line.

7. A system for propagating radio-frequency energy of a predetermined wavelength having, in combination, an unbalanced two-conductor transmission line, a balanced two-conductor transmission line, means for connecting one conductor of the unbalanced line by a singleconductor path of length less than an eighth of the said wavelength to one of the conductors of the balanced line at an intermediate point therealong that, with respect to the said one conductor of the unbalanced line, is substantially electrically symmetrically disposed between the ends of the balanced line, the said ends each being terminated in similar radiating elements to present substantially the same impedance at the said intermediate point, means for providing an electrical path between the other conductors of the lines, the said path being disposed in a region electrically isolated from the radio-frequency field between the conductors of the balanced line in order to prevent current flowing along the other conductor of the unbalanced line from influencing the radio-frequency field between the conductors of the balanced line, and the radiating elements surrounding the balanced and unbalanced lines.

8. A system for propagating radio-frequency energy of a predetermined wavelength having, in combination, an unbalanced coaxial transmission line, a balanced parallel-conductor transmission line, means for connecting the inner conductor of the coaxial line by a singleconductor path of length less than an eighth of the said wavelength to one of the conductors of the parallel-conductor line at an intermediate point therealong that, with respect to the said one conductor of the unbalanced line, is substantially electrically symmetrically disposed between the ends of the balanced line, the said ends each being terminated in similar radiating elements to present substantially the same impedance at the said intermediate point, means for providing an electrical path between the other conductors of the lines, the said path being disposed in a region electrically isolated from the radio-frequency field between the conductors of the balanced line in order to prevent current flowing along the outer conductor of the coaxial line from influencing the radio-frequency field between the conductors of the balanced line, the radiating elements being external to the balanced line.

9. A system for propagating radio-frequency energy of a predetermined wavelength having, in combination, an unbalanced coaxial transmission line, a balanced parallelconductor tarnsmission line, means for connecting the inner conductor of the coaxial line by a single-conductor path of length less than an eighth of the said wavelength to one of the conductors of the parallel-conductor line at an intermediate point therealong that, with respect to the said one conductor of the unbalanced line, is substantially electrically symmetrically disposed between the ends of the balanced line, the said ends each being terminated in similar radiating elements to present substantially the same impedance at the said intermediate point, means for providing an electrical path between the other conductors of the lines, the said path being disposed in a region electrically isolated from the radio-frequency field between the conductors of the balanced line in order to prevent current flowing along the outer conductor of the coaxial line from influencing the radio-frequency field between the conductors of the balanced line, and the radiating elements surrounding the balanced and unbalanced lines.

10. A system for propagating radio-frequency energy of a predetermined wavelength having, in combination, a pair of parallel conductors providing a balanced transmission line and at least one of which is hollow, an unbalanced coaxial transmission line disposed within the said one hollow conductor and extending coextensively therewith to a predetermined intermediate point thereof that, with respect to the inner conductor of the said coaxial line, is substantially electrically symmetrically disposed between the ends of the other of the pair of parallel conductors of the balanced line, the said ends each being terminated in similar radiating elements to present substantially the same impedance at the said predetermined intermediate point, an aperture in the said one hollow conductor near the said predetermined point, a single-conductor path extending from the inner conductor of the coaxial line through the aperture to a corresponding point of the other of the pair of parallel conductors, the inner surface of the said one hollow conductor and the coextensive outer conductor of the coaxial line being electrically contiguous, the radiating elements surrounding the lines.

11. A system for propagating radio-frequency energy of a predetermined wavelength having, in combination, a pair of parallel conductors providing a balanced transmission line and at least one of which is hollow, an unbalanced coaxial transmission line disposed within the said one hollow conductor and extending coextensively therewith to a predetermined intermediate point thereof that, with respect to the inner conductor of the said coaxial line, is substantially electrically symmetrically disposed between the ends of the other of the pair of parallel conductors of the balanced line, the said ends each being terminated in similar radiating elements to present substantially the same impedance at the said predetermined intermediate point, an aperture in the said one hollow conductor near the said predetermined point, a singleconductor path extending from the inner conductor of the coaxial line through the aperture to a corresponding point of the other of the pair of parallel conductors, the inner surface of the said one hollow conductor and the coextensive outer conductor of the coaxial line being electrically contiguous, the radiating elements being cylindrical antenna elements surrounding the lines.

12. A system for propagating radiotrequency energy having, in combination, a pair of parallel conductors, at least one of which is hollow, providing a balanced transmission line, means for supporting the balanced transmission line within an insulating housing coextensive therewith, an unbalanced coaxial transmission line disposed within a portion of the said one hollow conductor and extending coextensively therewith to a predetermined intermediate point thereof that, with respect to the inner conductor of the said coaxial line, is substantially elec trically symmetrically disposed between the ends of the other of the pair of parallel conductors of the balanced line, the said ends each being terminated in similar radiating elements to present substantially the same impedance at the said predetermined intermediate point, an aperture in the said one hollow conductor near the said predetermined point, a single-conductor path extending from the inner conductor of the coaxial line through the aperture to a corresponding point of the other parallel conductor, the inner surface of the said one hollow conductor and the coextensive outer conductor of the coaxial line being electrically contiguous, the radiating elements comprising conductive sleeves within the housing and connected to the balanced transmission line.

13. A system for propagating radio-frequency energy having, in combination, a pair of parallel conductors comprising a first transmission line, one of the conductors being hollow and of larger cross-section than the other, a coaxial transmission line disposed within the larger hol low conductor, means for connecting the inner conductor of the coaxial line by a single-conductor path to the other of the pair of parallel conductors at an intermediate point therealong that, with respect to the said inner conductor, is substantially electrically symmetrically disposed between the ends of the said other conductor of the said first transmission line, the said ends each being terminated in similar radiating elements to present substantially the same impedance at the said intermediate point, and the inner surface of the larger hollow conductor and the outer conductor of the coaxial line being electrically contrguous.

14. A system for propagating radio-frequency energy having, in combination, a hollow conductor, a conductor of smaller cross-section than the hollow conductor disposed on one side of the same to form a parallel transmission line therewith, at least one end of the smaller conductor being provided with a transverse connection to an extension of the smaller conductor disposed substantially on the opposite side of the hollow conductor, a coaxial transmission line disposed within the hollow conductor and extending therealong with the outer conductor of the coaxial transmission line and the inner surface of the hollow conductor being electrically contiguous, and a single-conductor path from a predetermined point of the inner conductor of the coaxial trans mission line to a corresponding point of the smaller conductor.

15. A system for propagating radio-frequency energy having, in combination, a hollow conductor, a conductor of smaller cross-section than the hollow conductor disposed on one side of the same to form a parallel transmission line therewith, each end of the smaller conductor being provided with a transverse connection to an extension of the smaller conductor disposed substantially on the opposite side of the hollow conductor, a coaxial transmission line disposed within the hollow conductor and extending therealong with the outer conductor of 9 the coaxial transmission line and the inner surface of the hollow conductor being electrically contiguous, and a single-conductor path from a predetermined point of the inner conductor of the coaxial transmission line to a corresponding point of the smaller conductor.

16. A system for propagating radio-frequency energy having, in combination, a hollow conductor, a conductor of smaller cross-section than the hollow conductor disposed on one side of the same to form a parallel transmission line therewith, at least one end of the smaller conductor being provided with a transverse connection to an extension of the smaller conductor disposed substantially on the opposite side of the hollow conductor, a coaxial transmission line disposed within the hollow conductor and extending therealong with the outer conductor of the coaxial transmission line and the inner surface of the hollow conductor being electrically contiguous, a single-conductor path from a predetermined point of the inner conductor of the coaxial transmission line to a corresponding point of the smaller conductor, and a plurality of antenna elements comprising spaced conductive sleeves surrounding all the transmission lines and connected to the smaller and hollow conductors.

17. A system for propagating radio-frequency energy having, in combination, a hollow conductor, a conductor of smaller cross-section than the hollow conductor disposed on one side of the same to form a parallel transmission line therewith, each end of the smaller conductor being provided with a transverse connection to an extension of the smaller conductor disposed substantially on the opposite side of the hollow conductor, a coaxial transmission line disposed within the hollow conductor and extending therealong with the outer conductor of the coaxial transmission line and the inner surface of the hollow conductor being electrically contiguous, a single-conductor path from a predetermined point of the inner conductor of the coaxial transmission line to a corresponding point of the smaller conductor, and a plurality of antenna elements comprising spaced conductive sleeves surrounding all the transmission lines and connected at adjacent edges alternately to the smaller-conductor extensions and the hollow condoctor.

18. A system 'for propagating radio-frequency energy having, in combination, a hollow conductor, a conductor of smaller cross-section than the hollow conductor disposed on one side of the same to form a parallel transmission line therewith, at least one end of the smaller conductor being provided with a transverse connection to an extension of the smaller conductor disposed substantially on the opposite side of the hollow conductor, a coaxial transmission line disposed within the hollow conductor and extending therealong with the outer conductor of the coaxial transmission line and the inner surface of the hollow conductor being electrically contiguous, a single-conductor path from a predetermined point of the inner conductor of the coaxial transmission line to a corresponding point of the smaller conductor, a plurality of antenna elements comprising spaced conductive sleeves surrounding all the transmission lines and connected to the smaller and hollow conductors, and a connection from the said extension of the smaller conductor to an upwardly directed further antenna element.

References Cited in the file of this patent UNITED STATES PATENTS 1,964,190 Bohm et al. June 26, 1934 2,581,352 Bliss Ian. 8, 1952 2,275,646 Peterson Mar. 10, 1952 2,646,505 Alford July 21, 1953 2,692,335 Alford Oct. 19, 1954 2,700,112 Iasik Jan. 18, 1955 2,727,232 Pryga Dec. 13, 1955 2,762,045 Stavis et a1. Sept. 4, 1956 FOREIGN PATENTS 601,353 Great Britain May 4, 1948 

